Liquefied natural gas, referred to in abbreviated form as “LNG,” is a natural gas which has been cooled to a temperature of approximately −162 degrees Celsius with a pressure of up to approximately 25 kPa (4 psig) and has thereby taken on a liquid state. Most natural gas sources are located a significant distance away from the end-consumers. One cost-effective method of transporting natural gas over long distances is to liquefy the natural gas and to transport it in tanker ships, also known as LNG-tankers. The liquid natural gas is transformed back into gaseous natural gas at the destination.
In a typical liquefaction process a compressor is used to deliver pressurized mixed refrigerant (MR) to a cold box, which in turn is used to cool a feed gas, such as a natural gas, to form a liquefied gas. Typically, LNG plants are designed to function optimally at one set of operating conditions, e.g., at one ambient temperature, and at one composition of natural gas (NG) feedstock. Altering the composition of the MR can change the optimal operating conditions of the plant, however, changes to the MR can only be made when the plant is shut down, e.g., on 6 to 12 month intervals. The MR composition is otherwise held constant during plant operation. Therefore, plants typically perform sub-optimally during the majority of their operation, which translates into reduced LNG production and/or increased costs. Accordingly, there is a need for methods and devices for modifying the optimal operating conditions of an LNG plant continuously.